Children in the same family often differ significantly in psychological characteristics and behavioral outcomes. They also show significant resemblances. However, the processes by which family environments are linked to sibling differences and similarities are only partly understood. Such understanding is critical to developmental theory and to theories of constitution-environment interactions. The purpose of this study is to investigate the shared and nonshared family experiences of siblings in relation to their characteristics and development. The research objectives are: to investigate child attributes (temperament, gender, age, and others) that relate to differential treatment by parents and to investigate links between siblings' shared and nonshared family experience and the developmental course of each sibling.